1. Field of the Invention
The present invention relates to a machine tool system, and more particularly to a method and apparatus for correcting deflection which the construction of the machine tool system may undergo due to the motion of a movable member of the machine tool system.
2. Description of the Related Art
A construction used with a large-sized machine tool system is inevitably long and very heavy. Therefore, it may undergo deflection, due to its own weight or due to the motion of the movable member of the machine tool system. If the construction of the machine tool system undergoes deflection, the working point on an object to be machined may be dislocated, lowering the machining accuracy.
According to one conventional correction method, this problem is solved by providing the sliding surfaces of the construction with correcting characteristics which are opposite to the deflection characteristics of the construction. However, a high-level technique is required in actually working the sliding surfaces to provide such correcting characteristics. In addition, the correction based on this method is not always reliable, since the correcting characteristics may include an error as a result of a change in the ambient temperature and since correction beyond the range of the correcting characteristics may be required in some cases.
Published Unexamined Japanese Patent Application No. 49-56274 discloses another correction method. According to this correction method, a hydraulic cylinder is arranged between an auxiliary beam and a cross beam of a machine tool system. If the cross beam, to which a tool rest is coupled, is deflected, this deflection is related to a position of the tool rest. On the basis of a signal output from a position detector for detecting the position of the tool rest, the pressure in the hydraulic cylinder is regulated such that the deflection of the cross beam is corrected. With respect to the method, it should be noted that the pressure in the hydraulic cylinder is regulated by use of a pressure-reducing valve operating on the basis of the signal output from the position detector. Therefore, the deflection which can be corrected by use of the method is limited to a linear one. In addition, satisfactory correction is impossible if the deflection of the cross beam exceeds a predetermined range of correction.
Published Unexamined Japanese Patent Application No. 56-33243 discloses still another correction method. According to this correction method, a hydraulic cylinder is arranged on both sides of the construction of a machine tool system. If the cross beam by means of which a tool rest is supported, is deflected, this deflection is applied to a cam plate. This cam plate is adapted to regulate the pressures in the two hydraulic cylinders in a manner to correct the deflection of the construction. With respect to the method, it should be noted that the correcting characteristics are constant due to the use of the cam plate. Therefore, if a change in the ambient temperature varies the relationships between the degree of deflection and the predetermined correction range, then correction cannot be performed.